1. Field
The present disclosure relates to a method for manufacturing nano-structures disposed to decrease surface density of semiconductor quantum structures which have quantum confinement effect like semiconductor quantum dots, and more particularly, to a nano-structure manufacturing method using a sacrificial etching mask.
2. Description of the Related Art
The semiconductor material shows features different from its bulk structure when quantum confinement effect is applied by forming nano-structures like a quantum well, a quantum wire, or a quantum dot. It is because state and distribution of the electrons in the semiconductor material structure change according to the degree of quantum confinement, and the features are physically and chemically distinguished from the state of bulk; for example, the change of band gap, the reinforcement of electron confinement, the formation of quantized internal energy levels, or the like.
Among them, compound semiconductor quantum dots have been recently studied to develop the laser which is insensitive to temperature, the photon detector which is sensitive to long-wavelength photons, the single photon emitting source which may be applied to the quantum encoded communication and the quantum calculation, or the like, by means of three-dimensional electron confinement.
In order to study such a semiconductor quantum dot, individual features should be revealed through measurement of an isolated single quantum dot. However, optical devices conventionally used for measuring features of a single quantum dot do not have enough resolution to distinguish signals from the adjacent quantum dots grown with a surface density higher than 1 μm−2. However, in the conventional quantum dot growth technique, the quantum dots are irregularly grown to have a surface density of 1 to 10 μm−2 in a statistical aspect even though the low density growth technique is applied.
In other words, in the above technique, generally, quantum dot specimens are grown several times so that a quantum dot specimen grown with a lower density is selected and used, or the entire surface of a quantum dot specimen is investigated so that a portion grown with a lower density is selected and used. Therefore, there is a limit in consistent reproduction of quantum dot specimens of a low surface density.
Therefore, as a method for additionally decreasing surface density of quantum dots in a specimen, an array of nano-structures may be manufactured to have a surface density which is lower than the surface density of the quantum dots in the specimen. Since the nano-structures are formed by etching layers including the quantum dots, quantum dots exist only inside the nano-structures and the surface density of the quantum dots are reduced. Representatively, there are methods for manufacturing nano-structures such as mesa or micropillar where each nano-structure has a diameter less than 1 μm and the surface density of the nano-structures is less than 1 μm−2.
However, the mesa or micropillar manufacturing method requires an additional process using the electron-beam (E-beam) lithography technique after the growth of a compound semiconductor specimen in order to form the nano-structures.
In the conventional E-beam lithography, negative E-beam resist (ER) is spin-coated on a grown specimen and then E-beam is irradiated to designate size and position of the nano-structures. As a result, the E-beam resist remains only at the E-beam irradiated points, and the remaining E-beam resist is utilized as a mask to form desired nano-structures by etching.